Process of reducing the viscosity of cellulose derivatives



Patented Jan. 11, 1938 t- UNITED STATES PROCESS OF REDUCING THE VISCOSITY OF CELLULO SE DERIVATIVES Kurt Thinius, Eilenburg, Germany, assignor to Deutsche -Celluloid-Fabrik, Eilenburg, Germany, a corporation of Germany No Drawing. Application June 18, 1936; Serial 4 Claims.

The present invention relates to the process for reducing-the viscosity of cellulose derivatives.

One of its objects is to provide a process for the reduction of the viscosity of cellulose derivatives whichmay be carried out at high pressure and at raised temperature. Another object is to provide a process for the reduction of the viscosity of cellulose derivatives which may be carried out while employing an oxidizing agent. Further objects will be seen from the specification 'following hereafter.

The extensive application of derivatives of the cellulose, of its esters with inorganic or organic acids, of mixed esters of these acids, of ethers and ether-esters for the production of films, sheets, lacquers, artificial silk, artificial bristles, artificial leather, plastic masses of all types, makes it necessary to impart special properties to these derivatives for the different purposes. Most of these special properties can be numerically defined by the: viscosity of the cellulose derivatives. The required viscosity of the cellulose derivatives may be obtained by different methods, either by taking a suitable starting material of low viscosity or, during the production of the cellulose derivatives, for instance by employing a raised temperature of reaction, by prolonging the time of reaction, by increasing the amount of the catalyst or by interposing a special process.

Mostly the required viscosity of the nitrocellulose is obtained by boiling it under pressure. During this reaction nitric acid and nitrous acid are split oif by hydrolysis, which undergo a decomposition into lower nitrogen oxides. At the end of boiling under pressure or, when working in accordance with known processes, during the boiling NO is detectable.

'According to the invention the properties of the nitrocellulose of low viscosity can be greatly improved by converting the nitrogen oxide formed during the hydrolysis by means of an oxidizing agent into N02 which now reacts during the boiling as an oxidizing agent with the pro-stabilized weakly acidulous nitrocellulose or with the unstable parts contained in it which are not clearly soluble in the ordinary solvents for nitrocellulose.

The most simple way of carrying out such an oxidizing pressure-boiling is to convert the N0 set free'by hydrolysis and disintegration into N02 by blowing in air during the pressure period. This oxidation by air can be performed for instance'by cooling the lower nitrogen oxides together with the water vapour in a cooling system outside the autoclave, built of acid resisting mate- ,rial, and bringing these oxidized products which are now dissolved in the condensate back to the autoclave by means of a suitable mechanism. During this circulation the air is introduced at a convenient spot, preferably before the condenser.

In Germany June 22, 1935 The nitric acid and the nitrous acid formed by mutual reaction with the water'vapour, cause a permanently, slightly acid reaction of the contents of the autoclave. An acidity corresponding to a pI-I-value of 3-4 has proved most advantageous for this oxidizing pressure boiling. Naturally it is possible to employ any other suitable oxidizing agent of the NO, for example oxygen or hydrogen-peroxide or a persalt.

The improvement of the nitrocellulose obtained by this oxidizing boiling under pressure is evident from the especially good clearness, color and the way of being filtered of the solutions produced from them which are to be used as a lacquer or as solutions for casting films. provement is obtained in the mechanical properties of the films and lacquer-layers produced from these materials. Furthermore all the nitrocellu loses produced by this oxidizing boiling under pressure show an increase in the stability as it is measured by the Bergmann-Junk-test and other tests'employed by the technician.

Furthermore it is of importance for the economy of the process, that the speed of reduction of the viscosity is increased by the oxidizing pressure boiling in such a way, that only of the time is required which is necessary to obtain the same viscosity by one of the known processes. Moreover a considerable improvement of the clearness and color of the solutions of these products is obtained within this essentially shorter time.

The reduction of viscosity accomplished by the oxidizing action of N02 permits of a reduction of the temperature of reaction, whereby, beside the heat economy, an improvement of the mechanical properties of the films and lacquer-layers produced from these materials is achieved. While this oxidizing pressure boiling is applicable independent of the starting material for the cellulose derivatives, it must be pointed out, that specially good results are obtained by using Wood-cellulose as a starting material. In the same manner the process is applicable for the treatment of film and celluloid Waste.

It has to be considered a special modification of the new process that hydrogen-peroxide and the oxidizing saponification product are brought to action with the material under pressure at the most suitable degree of acidity above mentioned.

With this procedure it is possible to slightly diminish the time of pressure and to decrease the temperature. When for instance pro-stabilized nitrocellulose is pressed at 135 C. after adding such an amount of hydrogenperoxide as an oxygen source that a solution of 0,2%-2% is formed in the autoclave, only half to one third of the pressure time is required which is necessary according to known procedures for instance according to German Patent 511,020. It has proved Moreover an im- 1 advantageous to carry through this modification of oxidizing pressure boiling under the simultaneous addition of stabilizers for the hydrogen peroxide, such as mixtures of H2504, NHO3 and oxalic acid. As the oxygen is liberated slowly with the use of such a stabilized hydrogen peroxide, it is possible to work with essentially smaller amounts of hydrogen peroxide and also with better economy.

After the pressure boiling it suffices to wash the nitrocellulose for a short time to remove the acids formed during the process whereafter it may be brought into use. This is a considerable improvement over the known processes which bring about the reduction of viscosity by means of concentrated salt solutions and in which a complete freedom from salt can only be attained by numerous washes. It has been shown that even smallest amounts of salt in the nitrocellulose have a detrimental eifect on the transformation of the nitrocellulose into celluloid or lacquers.

The process is not only applicable to nitrocellulose but to all materials which form oxidizable products during the pressure boiling for instance to nitroethylcellulose or nitroacetylcellulose.

The following are examples of carrying out my invention:

Example 1.-After washing into the autoclave, 50 kilos of nitrocellulose of the highest viscosity (K-1300) and pretreated in the ordinary way are boiled under pressure at 135 C. for one hour with 500 kilos: of water to which were added 3 kilos of H202 (calculated as A reduction of viscosity is achieved to a K-value of 800. (A definition of the K-value is given by Fikentscher in Cellulosechemie, Nr. 13, page 58, (1932)). The hydrogen peroxide is consumed at the end of the reaction. When working without hydrogen peroxide the double pressure time is necessary for obtaining the same reduction of viscosity. The solutions of the nitrocellulose treated according to this oxidizing pressure boiling process are distinguished by a remarkable clearness.

Example 2.After washing into the autoclave, 50 kilos of prestabilized nitrocellulose of highest viscosity (K-1300) are boiled under pressure at 135 C. for one hour with 500 kilos of water to which 1 kilo of hydrogenpero-xide (calculated as 100%) and as a stabilizer for it 500 g. H2SO4, 1 kilo HNOa and 200 g. oxalic acid aqua) were added; there is also effected a reduction of viscosity to a K-value of 800. The decrease of the nitrogen content is of the same order as at the boiling with water. The very clear solution produced from this product gives a film of high mechanical qualities with the following material characteristics (as compared with a film produced from a nitrocellulose obtained by the normal pressure processes).

Example 3.50 kilos of prestabilized nitrocellulose of highest viscosity, after being washed into an autoclave, are heated together with 500 kilos water under pressure for one hour at 125 C. During this time 250 to 300 liters of air are blown in by means of a suitable mechanism. A reduction of viscosity is obtained to a K-value of about 730. 7

Example 4.- 50 kilos of nitrocellulose together with 500 kilos of water, to which were added 2,5 kilos of ammoniumpersulfate are heated under pressure for two hours at C. The viscosity decreases from K-1300 to K-400. The solutions of this nitrocellulose are of specially clear and light colour.

Example 5.50 kilos of nitroethylcellulose of a K-value 950 are treated as in Example 1. A nitroethylcellulose of low viscosity is obtained with a K-value 620. In. the same manner the viscosity of the highly viscous nitroethylcellulose soluble in acetone can be reduced.

What I claim is:

1. In a process of treating cellulose derivatives containing nitro-groups .to clear and stabilize the same and to reduce the viscosity thereof which comprises heating the undissolved cellulose de' rivatives in an aqueousmedium under pressure at a temperature of from 106 C. to 150 C., the step of oxidizing the volatile products formed during said pressure heating, and using said oxidized products as oxidizing agents for the pressure heating.

2. In a process of treating cellulose nitrate to clear and stabilize the same and to reduce its viscosity which comprises heating under pressure at a temperature of 135 C. 50 kilos of prestabilized nitrocellulose of the highest viscosity (K-1300) together with 500 kilos of water the step of oxidizing the nitrogen oxide developed during the heating by addition of 3 kilos of hydrogenperoxide (100%) to nitrogenperoxide and using said nitrogenperoxide also as an oxidizing agent during the pressure heating.

3. In a process of treating cellulose nitrate to clear and stabilize the same and to reduce its viscosity which comprises heating under pressure for one hour at 135 C. 50 kilos of prestabilized nitrocellulose of highest viscosity (K- 1300) together with 500 kilos of water to which were added 1 kilo of hydrogen peroxide as an oxidizing agent and. 500 g. H2304, 1 kilo I-INO: and 200 g. oxalic acid as stabilizers for it, the step of oxidizing the developed nitrogen oxide by said hydrogen peroxide to nitrogen peroxide and using said nitrogen peroxide also as an oxidizing agent during the pressure heating.

4. In a process of treating cellulose nitrate to clear and stabilize the same and to reduce its viscosity which comprises heating 50 kilos of prestabilized nitrocellulose together with 500 kilos water for one hour at C. under pressure, the step of oxidizing the nitrogen oxide developed during the pressure heating to nitrogenperoxide by means of 250-300 liters of air and using 65 the nitrogenperoxide also as an oxidizing agent.

KURT THINIUS. 

